Process and apparatus for cutting or welding a workpiece

ABSTRACT

A metal jet cutting system, which includes a jetting heat, a heater and a power source, is used for modifying a workpiece. The jetting head includes a crucible and an inlet for receiving a feed stock of a conductive material. The heater melts the conductive material in the crucible to provide a conductive fluid, which exits the jetting head via an outlet. The power source, which is in electrical communication with the conductive fluid, increases the temperature of the conductive fluid. The conductive fluid is applied to the workpiece to modify the workpiece.

RELATED APPLICATIONS

This is a divisional of prior application Ser. No. 09/665,650, file onSep. 20, 2000, now U.S. Pat. No. 6,525,291 the entire disclosure ofwhich is incorporated by reference herein.

This application claims priority to and incorporates herein by referencein its entirety U.S. Provisional Application Serial No. 60/155,078,filed Sep. 21, 1999, entitled Process and Apparatus For Cutting OrWelding A Workpiece.

FIELD OF THE INVENTION

The invention relates to a process and an apparatus for cutting orwelding a workpiece.

BACKGROUND OF THE INVENTION

Oxyfuel cutting, plasma cutting, and laser cutting are three principalmethods used to thermally cut a metallic workpiece. Oxyfuel cutting ismainly used to cut mild steel where the benefits of the exothermicburning reaction of oxygen and iron are used to do the cutting. In thisprocess, the reaction rate and the resulting cutting rate is determinedby the diffusion rates of the reactants and the shear of the gas jet onthe liquid metal to remove it from the cut. For cutting a mild steelworkpiece having a thickness in the range from about 10 mm to about 12mm, typical cutting speeds range from about 0.5 to about 1.5meters/minute. Kerf widths vary from about 1 mm to greater than about 3mm.

In plasma cutting, the energy used to cut a workpiece is supplied by anelectric-arc-heated plasma gas jet which is directed toward or broughtin contact with the workpiece. The plasma cutting technique works on alltypes of electrically-conductive materials and, therefore, has a widerapplication range than oxy-fuel cutting. Typical plasma arc temperaturesare greater than 6000° C. During plasma cutting, metal from theworkpiece is removed from the kerf by the shear of the very highvelocity plasma-arc jet. Typical cutting speeds for plasma cutting aregreater than those of oxyfuel cutting A typical cutting speed forcutting ½″ mild steel with oxy-fuel is about 16 inches/min; whereas a200 Amp plasma system would typically cut that same size material at 80inches/min. Kerf widths for plasma cutting are about the same size orlarger then those for oxyfuel cutting. The relatively large kerf widthhas an adverse influence on the precision of the plasma cutting process.

In laser cutting, the energy used to cut a workpiece is supplied by alaser beam directed toward or brought in contact with the workpiece.Material is removed from the kerf by the shear from an assist gas jetdirected into the kerf. In laser cutting, kerf widths are narrow. Kerfwidths typically range from about 0.15 mm to about 0.5 mm. These narrowkerf widths consequently yield higher precision cutting than is possiblewith either oxyfuel or plasma cutting. However, in laser cutting, itbecomes difficult to remove the molten metal from the kerf as theworkpiece thickness increases. This limits the cutting speed and themaximum thickness capability for laser cutting. It is believed that thereason for this limitation is that the high gas velocity required toachieve sufficient gas shear creates supersonic shock waves a fewmillimeters into the kerf. These shock waves limit the gas shear and itsability to remove metal.

A fourth method for thermally cutting a workpiece is disclosed in U.S.Pat. No. 5,288,960. In this thermal-cutting method, a high temperatureliquid metal stream is directed at and impinges on the workpiece. Thetemperature of the stream exceeds the melting temperature of theworkpiece. The problem of removing the molten metal from the kerfbecause of limited gas shear encountered in laser cutting is thus easedby using a medium (i.e., liquid) with a higher specific density.Compared to laser cutting, higher cutting speeds, thicker workpiececapability, and equivalent high precision cuts can be realized with thisliquid-metal-stream cutting approach. However, because of the need tosupply a high speed liquid stream to the workpiece, at a temperaturegreater than the workpiece melting point, this approach has been limitedin its use for cutting certain metal. The material requirements for ahigh temperature, high pressure, liquid containment vessel severelylimits the practicality of cutting metals such as aluminum, stainlesssteel and mild steel, where typical melting temperatures are 660° C.,1400° C. and 1550° C., respectively.

Several methods are used to thermally weld a workpiece. The most widelyused welding processes use heat sources to cause localized heating oftwo or more workpieces, allowing them to melt and flow together. Afiller metal generally is added to the weld area in order to supplysufficient material to fill the joint and to increase mechanicalstrength. For example, a fillet weld generally forms a radial sector ofadditional material over a weld groove when completed. When the weldingprocess is progressing, a molten pool of workpiece forms and a fillermaterial is moved along the welding front. When the welding heat sourceis removed, the molten metal solidifies, and the parts are fused orwelded together. Common heat sources used to provide heat to melt theworkpieces are DC or AC electrical arc, oxy-fuel gas flame, and laserbeam.

SUMMARY OF THE INVENTION

An objective of this invention is to provide a very high energy densityfluid stream which can be used in materials working processes. Anotherobjective of this invention is to provide a process and an apparatus forthermally cutting workpieces at high speed and high precision over alarge range of workpiece thicknesses. Another objective of thisinvention is to provide a process and an apparatus for thermally weldingworkpieces at high speed and high precision. Another objective of thisinvention is to thermally cut and/or weld non-metallic and/ornon-conducting materials. A further objective of this invention is toprovide a process and an apparatus of cutting and/or welding which issimple in design, easy to operate and maintain and cost effective touse.

In one aspect, the invention features a system for modifying aworkpiece. The system comprises a dispenser and a power source. Thedispenser comprises an electrically conductive material for forming ajet stream. The power source is electrically coupled to the jet stream.

In one embodiment, the dispenser comprises a jetting head. For example,the jetting head can comprise a crucible. A heater can be coupled to thecrucible. The heater can comprise one of an AC resistance heater, a DCresistance heater, an induction heater, or a combustion burner-heaterarrangement. The heater can comprise an induction heater coil wrappedaround the crucible. In one example, the induction heater coil wrappedaround a first end of the crucible has a closer packed relationship thanthe induction coil wrapped around a second end of the crucible. Inanother example, the induction heater coil wrapped around a first end ofthe crucible has a smaller diameter than the induction coil wrappedaround a second end of the crucible. The system can further comprise adepressurizing vent in communication with the pressure containmentvessel. The crucible can comprise a refractory material. For example,the crucible can comprise a material selected from one of zirconiumdiboride, alumina, zirconia, boron nitride, and graphite. The conductivematerial for forming the jet stream can comprise a metal.

The jetting head can comprise an inlet for receiving a feed stock of theconductive material. In another embodiment the jetting head can comprisemultiple inlets for receiving multiple feed stocks of conductivematerial. The jetting head can further comprise a feed stock valve. Thejetting head can comprise a pressure containment vessel and a heaterdisposed inside the pressure containment vessel. The system can furthercomprise a pressurizing gas source in communication with the pressurecontainment vessel. The jetting head can comprise an electrode disposedinside the crucible for establishing an electrical connection with thejet stream.

The jetting head can comprise an exit orifice. In addition, the jettinghead can further comprise a plug. In this embodiment, the jetting headcan comprise a plug rod disposed above the exit orifice. The jettinghead can further comprise a nozzle. The nozzle can comprise a diskhaving a conical opening. The jetting head can further comprise a nozzleand a nozzle cap detachably attached to the pressure containment vesseladjacent the nozzle. In one embodiment a filter can be placed in serieswith the nozzle. In another embodiment the crucible has a conductivefluid filter.

In one embodiment, the system for modifying a workpiece furthercomprises a first lead electrically coupled to the power supply and awork piece and a second lead electrically coupled to the power supplyand a conductive fluid disposed in the crucible. In another embodiment,the system of can further comprise a first lead electrically coupled tothe power supply and a work piece clamp and a second lead electricallycoupled to the power supply and a conductive fluid disposed in thecrucible. In still another embodiment, the system can further comprise afirst lead electrically coupled to the power supply and a currentcollector. For example, the current collector can comprise a vessel.

In still another embodiment, the system can further comprises a firstlead electrically coupled to a first power supply and a first feedstockand a second lead electrically coupled to the first power supply and asecond feedstock. The first and second feedstocks making electricalcontact with the conductive fluid disposed in the crucible. The twofeedstocks are heated by passing current between them. A second powersupply comprises a first lead electrically coupled to the work piece anda second lead electrically coupled to the power supply and a feedstockof the first power supply.

The jetting head can further comprise a shield assembly supporting thenozzle. The shield assembly can comprise a disk having a plurality ofinlet orifices for introducing a shield gas to the jet stream.

In another aspect, the invention features a metal jet cutting system.The system comprises a jetting head including an exit orifice fordispensing a jet stream of a conductive fluid and a power sourceelectrically coupled to the jet stream for providing a current to thejet stream to increase a temperature of the jet stream above a meltingtemperature of the conductive fluid.

In still another aspect, the invention features a process for modifyinga workpiece. According to the process, a jet stream comprising aconductive fluid is provided. An electrical current is passed throughthe jet stream. The jet stream is directed at the workpiece formodifying the workpiece.

The jet stream can be heated in a variety of ways. A current can beapplied to the jet stream through an electrode coupled to the conductivefluid and a current collector disposed near the workpiece. A current canbe applied to the jet stream through an electrode coupled to theconductive fluid and a workpiece clamp. The jet stream can be heatedthrough ohmic power dissipation. The jet stream can be heated to atemperature substantially above a melting temperature of the conductivefluid. A temperature of the jet stream can be increased up to about1000° C. above a melting temperature of the conductive fluid. The jetsteam can be a continuous jet stream, a pulsed jet stream, a steady jetstream, or an unsteady jet stream.

In one embodiment the heater of the crucible is an induction heaterwhere the characteristic frequency of the induction heater can becalibrated to the level of a conductive fluid in the curcible.

In one embodiment, the feed stock and the workpiece comprise the sametype of material. Alternatively, the feed stock can the workpiece cancomprise different types materials. For example, the feed stock cancomprise aluminum and the workpiece can comprise stainless steel. Thefeed stock can be a conductive fluid. Alternatively, the feedstock canbe heated to form a conductive fluid. In one example, the feed stock isa metal such as aluminum, iron, an iron containing compound, tin,nickel, titanium, gold, platinum, silver, magnesium, copper, mild steelor aluminum-iron alloy. The feed stock can comprise a wire, bar, orpowder. In still another embodiment the feedstock can comprise a wire orbar and also serve as an electrical contact between a power source andthe conductive fluid. More than one feed stock can be in contact with anelectrical power source. The feed stock can comprise a plurality ofnon-melting particles. The non-melting particles can be abrasive. Thefeed stock can have a low melting point and a high boiling point.

The exit orifice of the crucible can be plugged while providing the feedstock and the exit orifice can be unplugged while the conductive fluidpasses through the exit orifice. A vacuum can be provided to the jettinghead to plug the exit orifice. A levitation force can be provided to theconductive fluid to plug the exit orifice.

In one embodiment, the jetting head is pressurized while passing theconductive fluid through the exit orifice. For example, the jetting headcan be pressurized by supplying an inert gas.

In another aspect, the invention features a crucible for a metal jetcutting system. The crucible comprises side walls and a base. Thecrucible is electrically conductive and is resistant to dissolving inthe presence of a metallic melt. The crucible can be formed from azirconium containing compound. The crucible can also be formed fromzirconia diboride or yitria-stabilized-zirconia.

In another aspect, the invention features a nozzle for a metal jetcutting system. The nozzle comprises a disk-structure having an orifice,wherein the orifice is located at a center of the disk-structure. Thenozzle is electrically conductive and is resistant to dissolving in thepresence of a metallic melt. The nozzle can be formed from a zirconiumcontaining compound. The nozzle can also be formed from zirconiumdiboride.

Various parameters can be controlled when the process of the presentinvention is performed. For example, a pressure in the jetting head, atemperature of the conductive fluid, a depth of penetration of the jetstream and/or a velocity of the jet stream can be controlled.

In one embodiment, the workpiece can be cut, marked or pierced.Alternatively, the workpiece can be welded. For example in welding, afirst workpiece having a first tapered edge and a second workpiecehaving a second tapered edge are provided. The first tapered edge ispositioned adjacent the second tapered edge to provide a groove. The jetstream is directed at the groove to fill the groove. Directing the jetstream at the groove can melt a portion of the workpiece forming amolten pool in the groove. Cooling the molten pool welds the firstworkpiece and the second workpiece.

In one embodiment, a workpiece can be modified by lowering a meltingpoint of the workpiece. The melting point can be lowered by forming analloy of the feed stock material and the workpiece material on a surfaceof a portion of the workpiece. The process of modifying a workpiece canfurther include providing a shielding gas to shield the jet stream.

In one embodiment, the process of modifying the workpiece can be used tomodify an insulative material. When modifying an insulative material, acurrent collector comprising a conductive material can be disposedunderneath the workpiece. The current collector forms an electricalcontact with the jet stream.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the presentinvention, as well as the invention itself, will be made fullyunderstood from the following description and embodiments, when readtogether with the accompanying drawings, in which:

FIG. 1a shows a schematic view of an apparatus for cutting a workpieceaccording to one embodiment of the invention.

FIG. 1b shows an inside view of the jetting head of FIG. 1a according toone embodiment of the invention.

FIG. 1c shows a detailed cross-sectional view of the nozzle area of thejetting head of FIG. 1b.

FIG. 2a shows a workpiece for welding according to one embodiment of theinvention.

FIG. 2b illustrates welding the workpiece of FIG. 2a according to oneembodiment of the invention.

FIG. 3 shows a schematic view of an apparatus for cutting a workpieceaccording to another embodiment of the invention.

FIG. 4a shows a cross-sectional view of the jetting head according toanother embodiment of the invention.

FIG. 4b shows a detailed cross-sectional view of the nozzle area of thejetting head of FIG. 4a.

FIG. 5a shows a detailed cross-sectional view of the jetting headaccording to another embodiment of the invention.

FIG. 5b shows a schematic view of an apparatus for cutting a workpieceaccording to one embodiment of the invention.

DETAILED DESCRIPTION

In one aspect, the invention features a process and an apparatus, inwhich a workpiece is either cut or welded by an impinging, fine streamof high temperature liquid metal working fluid. In one embodiment, theliquid metal working fluid is formed by melting and then holding theworking fluid in a heated crucible. The temperature of the metal workingfluid in the crucible is maintained at a temperature above its meltingpoint. During operation, the working fluid is heated under pressure inthe crucible and subsequently directed toward the workpiece as a jetstream passing through a nozzle orifice located at an outlet of thecrucible.

In one embodiment, an electrical power source is connected between theliquid metal working fluid in the crucible and anelectrically-conducting workpiece or an alternative electrode positionedbeneath the cut workpiece. During operation, an electric current ispassed between the liquid metal working fluid in the crucible and theworkpiece or the alternative electrode via the liquid metal stream. Thepassage of current through the small diameter liquid stream heats thejet stream by ohmic (I²R) power dissipation (where I represents theelectrical current and R represents the electrical resistance). Thetemperature increase of the stream, enroute to the workpiece, isdependent on: a) the electrical power input to the stream; b) the streammass flow rate; and c) the heat capacity (specific heat) of the liquid.Since the power input to the stream is an independent variable, whichmay be operator controlled, energy can be added to the stream toincrease its temperature, as desired. This reduces the high temperaturedemands from crucible construction materials and makes it feasible tocut or weld materials with high melting-point temperatures using workingfluids that have much lower melting points. High melting point workpiecematerials can be worked (either cut, welded or brazed) by addingwhatever temperature is required for the working fluid enroute to theworkpiece. For example, mild steel and stainless steel, which haveapproximate melting points of 1550° C. and 1400° C., respectively, canbe cut with low melting point working fluids such as aluminum or tinalloys, which have approximate melting temperature of 660° C. and 232°C., respectively, by adding whatever additional temperature is requiredby I²R power dissipation in the liquid metal stream.

As an illustration of the invention's improvement in the cuttingprocess, the following Table 1 compares the typical theoreticalcross-sectional power densities of the above mentioned cuttingprocesses. The cutting speeds and process parameters are assumed to betypical for each process. The power density is calculated for eachprocess as the energy passing through a cross-sectional diameter equalin size to the kerf width associated with each process. As can be seenin Table 1, the process of the present invention delivers, by far, morepower per unit area than any of the other processes. This power densityis an indication of the ability of the process of the present inventionto deliver melting energy to a workpiece kerf.

TABLE 1 Typical Power Densities (W/mm²) for Cutting Processes (cutting½″ mild steel, 1520° C. melt temp) Cutting Process Power Density 1.Oxy-fuel (oxygen-iron burning reaction, 2 mm kerf) 14 2. Plasma (200 A,100 V, 4 mm kerf) 1,600 3. Laser (3 kW with oxygen assist, 0.4 mm kerf)24,000 4. Aluminum Jet (200 μm nozzle, 14,600 1750° C. jet, 0.2 mm kerf)5. Aluminum Jet w/ I²R Heating (200 μm nozzle, 53,000 1750° C. jet + 1.2kW I²R, 0.2 mm kerf) 6. Aluminum Jet w/ I²R Heating (200 μm nozzle,30,000 900° C. jet + 2.1 kW I²R, 0.2 mm kerf)

As shown in the Table 1, the initial temperature of the aluminum jet(900° C.) can be less then the melting temperature of the workpiece(1520° C.), with the additional temperature needed to cut the workpiececoming from the added I²R power dissipation.

Referring to FIGS. 1a, 1 b, and 1 c, an apparatus for cutting or weldinga workpiece includes a jetting head (9), a crucible neater power supply(34), a stream heating power supply (54), and a pressurizing gas source(22). The crucible power supply (34) is electrically connected to thejetting head (9) through a pair of leads (32) (33). The stream heatingpower supply (54) is electrically connected to the jetting head (9)through a negative lead (52) and to a workpiece (70) through a positivelead (53). Gas from the gas source (22) is supplied to the jetting head(9) through a pressurizing gas source interconnecting piping (18), apressurizing gas source regulator (23), and a pressurizing gas sourceon/off valve (20). The jetting head (9) is de-pressurized through ade-pressurizing vent (25), a de-pressurizing vent interconnecting piping(19), and a de-pressurizing vent on/off valve (21).

The jetting head (9) includes a pressure containment vessel (10), acrucible (11), a crucible heater (30), a feedthrough (30 a) for the pairof leads (32) (33), a stream heating electrode (50), a feedthrough (50a) for the negative lead (52), a plug rod (26), a plug rod actuator (26c), a plug rod seal (26 e), a plug rod ball (26 a), a plug rod ball seat(26 b), a crucible compliant top seal (16), a crucible bottom sealinggasket (15), a nozzle disk (12), a nozzle disk sealing gasket (14), anozzle nut (13) and a molten metal working fluid (80).

The feedstock (87) is fed into the jetting head (9) through thefeedstock inlet (17 c). The feedstock (87) can be introduced into thejetting head (9) in either solid form as shown, where the melting andliquid forming takes place in the crucible (11), or the feedstock can beintroduced in liquid form, where the melting and forming of the liquidmetal takes place outside of the jetting head (9), prior to itsintroduction into feedstock inlet (17 c). In either case, workingmaterial moves into the jetting head (9) through the feedstock passage(17 d) and into the crucible (11). During operation, the heated crucible(11) maintains the feedstock (87) in a molten state. The feedstock (87)is fed through the opening (17 e) in the feedstock valve (17) when theopening (17 e) is aligned with the passage (17 d). When closed byfeedstock valve actuator (17 b), the opening (17 e) no longer alignswith the passage (17 d), the passage (17 d) is then gas-tight sealed byseals (17 a). The feedstock valve (17) allows the interior of thejetting head (9) to be pressurized.

The crucible (11) is heated by the crucible heater (30). The crucibleheater (30) can be any heater which heats the crucible (11) to thedesired temperature. For example, the heater (30) can be AC or DCresistance heater, an induction heater, or a combustion burner-heater.In one embodiment, an AC electrical resistance heater is used. Thisheater has power connections (32) and (33), which are, in turn connectedto the crucible heater power supply (34). Power leads (32) and (33) passthrough the pressure vessel top (10 b) via crucible heater electricalfeedthrough (30 a). This feedthrough (30 a) makes a gas pressure sealwith the pressure vessel top (10 b) and insulates the leadselectrically.

In one embodiment, the crucible (11) has side walls and a base. Thecrucible (11) is made of a refractory material, which is compatible withthe high temperature molten working fluid so that the crucible isresistant to dissolving in the presence of a metallic melt. Examples ofsuitable crucible materials include, but are not limited to, zirconiumcontaining compounds, alumina and zirconia ceramics of variouscompositions, boron nitride materials of various compositions, boronnitride, boron nitride-zirconia-silicon carbide, silica, zirconiumdiboride, Yttria-Stabilized-Zirconia, Magnesia-Stabilized-Zirconia,Calcia-Stabilized-Zirconia, Cubic Zirconia, silica composites, andgraphite. In one embodiment, the crucible material can be boron nitridematerials, such as Grade ZSBN material, which is made up of boronnitride-zirconia-silicon carbide, supplied from The Carborundum Companylocated in Amhurst, N.Y. In another embodiment, the crucible is made ofgraphite. Since graphite is electrically conductive it may be desirableto electrically isolate the crucible (11) from the pressure containmentvessel (10) and the crucible heater (30). In one embodiment, thecrucible (11) is electrically isolated. The bottom end of the crucible(11) is sealed by the crucible bottom gasket (15) located on the bottomof the crucible (11), between the crucible (11) and the pressure vesselbottom (10 a). In one detailed embodiment, the gasket (15) is made ofhigh temperature alumina refractory gasket material, which is anelectrical insulator. The gasket (15) is loaded under pressure from thecompliant seal (16) located on the top of the crucible (11), between thecrucible (11) and the top of the pressure vessel (10 b).

In one embodiment, the outlet for the liquid metal working fluid issealed by the movable plug rod ball (26 a), which is in a sealing fitrelationship with the plug rod ball seat (26 b). The plug rod actuator(26 c) applies a sealing force through arm (26 d) to the plug rod (26),which forces the plug rod ball (26 a) on to the plug rod ball seat (26b) during times of no liquid metal flow. Since the crucible (11), theplug rod (26), the plug rod ball (26 a) and the plug rod ball seat (26b) are in contact with the liquid metal (80), the construction materialsfor these components must be chosen so that they will withstand themechanical and thermal stresses at high temperature and resist corrosionin a chemically reactive environment. In addition, the plug rod ball (26a) and plug rod ball seat (26 b) must be made of materials which willtogether make a good intermittent seal of the liquid metal underpressure. It is anticipated that working pressures will range from about50 to about 5000 psi. In addition, in one embodiment, the plug rod (26)and the plug rod ball (26 a) are electrically isolated and/or made ofelectrically non-conducting material in order to electrically isolatethe working fluid resistance heating power supply (54) from othercurrent paths. The electrical isolation of the crucible and plug rodparts would not be necessary if the entire jetting head assembly wereallowed to ‘float’ electrically at the same potential as the crucible.The plug rod (26) is sealed on the pressure vessel top (10 b) by plugrod pressure seal (26 e).

In one embodiment, the stream-heating power source (54) is connected tothe working fluid (80) by an electrode (50) which extends down into thecrucible (11) and is generally surrounded by and in good electricalcontact with the liquid metal working fluid (80). The electrode (50) isconnected to the power supply (54) by a connecting wire (52), whichpasses through the top (10 b) of the pressure vessel via the feedthrough(50 a). This feedthrough (50 a) makes a gas pressure seal and electricalinsulation with the top (10 b) of the pressure vessel. The oppositepolarity of the stream heating power supply (54) is connected via cable(53), switch (54 a) and electrical clamping means (55) to workpiece(70).

FIG. 1c shows an enlarged view of the nozzle area. The nozzle areaincludes a nozzle disk (12). The nozzle disk (12) is a cylindrical diskhaving a top (12 a), a bottom (12 b) and an outside diameter wall (12c). An orifice (5) is formed at the top (12 a) of the nozzle disk (12)on the centerline. The orifice (5) has a bore (5 a) and a length (5 b).A conical opening (5 c) extends from the outlet of orifice (5) to thebottom (12 b) of the nozzle disk (12). Typical orifice diameters canrange from about 25 to 500 μm. The nozzle disk (12), in one embodiment,is made out of a material which is electrically conductive and resistantto dissolving in the presence of a metallic melt, and the nozzle disk(12) can be formed with a precise, small diameter orifice and which canfunction in the severe environment of high temperature liquid metals.The nozzle disk (12), like the crucible (11) can also be made out ofzirconium containing compounds such as Yttria-Stablized-Zirconia,Magnesia-Stablized-Zirconia, Calcia-Stablized-Zirconia, boron nitride,boron nitride-zirconia-silicon carbide, Cubic Zirconia, Alumina, Silica,Silica Composites, Zirconium Diboride. In one detailed embodiment, thematerial for the nozzle disk (12) is sapphire (e.g., alumina). Thenozzle disk (12) is held against the nozzle sealing gasket (14) bypressure applied by a nozzle cap (13). The nozzle cap (13) has athreaded portion (13 a) which is attached to the bottom (10 a) of thepressure vessel on threaded portion (10 c). In one embodiment, thenozzle sealing gasket (14) is made of a material which can function inthe severe environment of high temperature liquid metals. For example,the gasket material can be graphite, such as the ‘Calgraph™’ materialsupplied by SGL Technic Inc. of Valencia, Calif.

The outside boundary of the jetting head interior is defined by theinside wall of the pressure containment vessel (10). This pressurevessel (10) must be made of material which can maintain high strength athigh pressure and elevated temperature, such as ‘Inconel™ 600’, which isa high nickel, super alloy available from the Inco Alloys InternationalCo. The pressure containment vessel (10) is pressurized through apressurizing gas source piping (18) which is connected to thepressurizing regulator (23) and the pressurizing gas source (22). Anon/off valve (20) is located some where along the pressurizing gassource piping (18). The pressure containment vessel (10) isde-pressurized through the de-pressurizing gas vent piping (19) which isconnected to the de-pressurizing gas vent (25). An on/off valve (21) islocated somewhere along the de-pressurizing gas vent piping (19). Theembodiment of FIG. 1b is designed so that the walls of the hightemperature crucible are not subjected to the high stresses caused bythe periodic pressurization of the jetting head (9). This isaccomplished by allowing the pressurizing gas flow to have access toboth the inside wall (11 a) and the outside wall (11 b) of the crucible(11). The pressurizing gas is allowed to flow freely through gaspassages (11 c) of the crucible (11). The internal cavity (8), which isall of the free space in the jetting head between the outside ofcrucible (11) and the interior walls of the pressure containment vessel(10) acts as a very effective thermal insulation barrier. This space,however, acts as a gas capacitance when charging and discharging thevessel with high pressure. In order to minimize this capacitance, theinternal cavity (8) may be filled with a non-porous thermal insulation.

In one embodiment, feedstock (87) is fed into the jetting head (9)during times when the jetting head is not under pressure. The feedstockis held in crucible (11) and is then melted if the feedstock is fed inas a solid, and is maintained in molten state.

When the jetting head (9) is powered up, in preparation for cutting, thecrucible power supply (34) is turned ‘ON’ by closing switch (34 a), thussupplying power to the crucible heater (30). The crucible heater (30)will, by controls not shown, maintain the temperature of the workingfluid (80) at a predetermined temperature somewhere above its meltingpoint. The predetermined temperature is set by electronic monitoringcontrols which use feedback from temperature sensors located in or nearthe molten metal working fluid. This electronic control system andtemperature sensors are not shown but are commercially available.

In one embodiment, an induction heater is used as a crucible heater(30). The induction heater can detect changes in the level of the moltenmetal working fluid in the crucible. A characteristic frequency of theinduction heater changes with the level of the molten metal workingfluid. In an induction heater, the material to be heated is coupled tothe heater's coil by the magnetic fields inside the coil. The presenceof the material and of the eddy currents induced in the materialinteract with and change the magnetic fields from the coil compared towhat the fields would be without any material inside the coil. Theadditional impedance of the material changes the total impedance of thecoil. The change in impedance of the coil changes the Q of the circuitand its resonant frequency. Therefore, the induction heater wouldoperate at different frequencies for conditions where material ispresent or absent inside the coil. Similarly, varying amounts ofmaterial inside the coil would result in varying shifts in frequency.The characteristic frequency can be monitored and calibrated to measurethe level of the molten metal working fluid.

The molten metal working fluid (80), which is formed from the feedstock(87) is specifically chosen for the particular application of interest.Although the working fluid is referred to as ‘metal’ the working fluidcan, in fact, be any electrically conductive fluid which will producethe desired effects on the workpiece. Some materials that can be usedfor the feedstock (87) include mild steel, aluminum, aluminum alloy,tin, stainless steel, iron, cast iron, tool steel, copper, zinc, gold,silver, nickel, titanium, magnesium or platinum. For example, when thedesired effect is to cut mild steel or stainless steel, the workingfluid may be an aluminum or aluminum-iron alloy.

Aluminum and aluminum alloys have several properties that make them goodchoices for the working fluid; such alloys have low melting pointtemperature, high boiling point temperature, high specific heatcapacity, high thermal conductivity and, a relatively low cost perkilogram. The melting point of pure aluminum is approximately 660° C.,the melting point of aluminum-iron alloys (or metal mixtures) vary fromapproximately 660° C. to 1540° C. depending on the amount of iron in themixture. The melting point of an aluminum-iron mixture with 90% aluminumcontent is approximately 800° C.

A major benefit of the present invention is the ability to use a workingfluid at such temperatures because it makes possible the use of a numberof available refractory materials for the crucible construction. Becausepure iron melts at about 1540° C., it is obvious that additionaltemperature must be added to the stream, enroute to workpiece in orderto cut. In addition, there is another benefit of using aluminum oraluminum alloys as the working fluid. That is, the temperature of analuminum-iron alloy has a lower melting temperature then pure iron (orsteel). Therefore, to the extent that the alloying process speed is fastenough, there will be this additional alloying process mechanism helpingthe cutting process when the stream combines (alloys) with a highermelting point workpiece metal. The alloying process, in general, willhelp the cutting process of all workpiece metals with melting pointshigher then that of the cutting stream by, in effect, lowering themelting point temperature of the workpiece metal in contact with thecutting (and alloying) stream.

As another example, a stainless steel workpiece could be cut using aworking fluid which consists of a compound material, such as, analuminum-magnesium alloy which also contains disperse amounts of fineceramic particles, such as 0.5-25 μm alumina or zirconia particles. Thiscutting fluid has the advantage of having non-melting particlesdispersed throughout the fluid to serve as abrasives to assist in thecutting process.

The present invention is not limited to be used with low meltingtemperature metal as the working fluid. For example, a mild steelworkpiece can be cut with a mild steel, a cast iron, a tool steel or apure iron working fluid. This choice of cutting fluid has thedisadvantage of a high melting point. However, there are a few cruciblematerials which can withstand temperatures around the melting point (orfluidization) temperature of iron and since any temperature above themelting point that is required can be added outside of the crucible,with the I²R power dissipation, the use of pure iron as cutting fluid ispossible in the present invention, and may be desirable in some cases.One benefit of using a mild steel or iron as a cutting fluid is thatenroute oxide formation will not adversely affect the fluidity of thestream; iron oxide has a lower melting point then iron itself. Some highcarbon steels have melting points less then that of pure iron which,therefore, make them candidate choices for cutting fluids. Other choicesfor cutting fluids for use in cutting mild steel include AISI 1006through AISI 1095 steels, cast irons, and tool steels. In anotherexample, if the workpiece to be cut is an aluminum alloy such as 6061,the working fluid can be a pure aluminum or an aluminum alloy. As stillanother example, if the workpiece to be cut is tin, the working fluidcan be tin. In general there may be an advantage for the working fluidmaterial to be the same material as the workpiece. For example whencutting, there would be no discernable metallurgical differences betweenthe base metal of the workpiece and the metal on the cut face. Inanother example, when cutting 316 stainless steel there would be anadvantage in using 316 stainless steel as the working fluid material inthat the same alloying elements would exist through-out with no changein the area of the cut.

Just prior to the beginning of a cutting operation, the followingconditions exist: a) the plug rod actuator (26 c) is in the offcondition and the plug rod ball (26 a) is sealing against the plug rodball seat (26 b); b) the feedstock valve (17) is closed and valve seals(17 a) are sealing passage (17 d) from the outside environment; c) thede-pressurizing gas venting valve (21) is in the ‘off’ condition and theventing path is closed; d) the pressurizing gas valve (20) is in the‘off’ condition and the gas path to the pressurizing gas source isclosed, and the pressurizing gas source is ready to supply gas to thejetting head; e) crucible heater power supply (34) is in the ‘on’condition, switch (34 a) is closed, and crucible heater (30) issupplying heat to crucible (11); f) the stream heating power supply (54)is turned ‘on’ and switch (54 a) is closed so that the power supply isapplying an electrical potential between the liquid metal fluid (80) andthe workpiece (70).

The cutting operation is accomplished by first opening the pressurizinggas source valve (20) which pressurizes the interior of the pressurevessel (10), including the inside of the crucible. The pressurizing gasis selected to be non-oxidizing and inert to reactions with the moltenmetal. Possible choices for the pressurizing gas include argon,nitrogen, helium, and argon with some hydrogen. In one embodiment, thepressurizing gas is argon with 5% hydrogen added. The purpose of thehydrogen is to make the pressurizing atmosphere slightly ‘reducing’ inorder to inhibit oxide formation. A special benefit of using iron as theworking fluid is that the presence of oxygen in the pressurizing gaswill not adversely affect the fluidization process since iron oxide, ifformed, will be fluidized along with the pure iron. The presence ofoxygen may, however, be undesirable for other components of the jettinghead such as the crucible and/or sealing gaskets. Subsequently, the plugrod actuator (26 c) is energized, which lifts by plug rod (26). The plugrod ball (26 a) is thereby lifted from the seat (26 b). As shown in FIG.1c, liquid metal fluid (80) flows through nozzle orifice (5), forming astream of liquid metal (82). When the stream contacts the workpiece(70), current will immediately begin to flow from the stream heatingpower supply (54) through the stream (82). This current flow immediatelyraises the stream temperature. As the high temperature stream impingeson the workpiece, it melts and erodes a pit until finally the heatedstream penetrates all the way through the workpiece. At this point theworkpiece has been pierced by the jet. Then finally relative movement(72) between the workpiece and the jetting head is started. Theseactions together cause the workpiece to be cut. The relative movementcontinues until the desired shape has been cut. At which point therelative movement can be stopped and stream (82) can be turned off by:a) opening switch (54 a) which stops the current flow through thestream; b) de-energizing actuator (26 c) which lowers plug rod (26),forcing plug rod ball (26 a) on to seat (26 b); c) de-energizing(closing) the pressurizing valve (20); d) energizing (opening) ventingvalve (21) which allows the pressurizing gas to flow out of the pressurevessel (10) through vent (25). The cutting sequence is then reset forthe next cut by again closing switch (54 a) so that the power supply isapplying an electrical potential between the liquid metal fluid (80) andthe workpiece (70). When it is desired to make the next cut the samesequence as above is followed. During a cutting or welding process thecurrent flowing through the jet to the workpiece can sometimes form aplasma arc at or near the workpiece surface. This plasma arc formationcan be detrimental to the cutting or welding process and may cause theprocess to become erratic resulting in poor cut or weld quality. It isimportant that steps be taken in controlling of the cutting or weldingprocess to limit the arcing to a very minimum, or if possible, totallyeliminate the arcing. One such step is to ensure the quality of the jetstream by employing filters to the working fluid prior to forming thejet. Filters for molten metals are commercially available. For example,filters for made of a typical composition of 93% zirconia, 5% magnesiaand <2% alumina-silicates and other compounds are made for mild steelfiltering and are available form the SELEE Corp of Hendersonville, N.C.

The following table summarizes results from cutting various materialsusing tin jet in accordance with the present invention. The I²R powerwas added to the tin jet via a DC power supply.

Liquid Metal Jet Cutting with Added I²R Heating Tin jetting material 250micron diameter nozzle 400 C. vessel temperature 400 psi vessel pressureMaterial Material Power Current Cut Speed Stand-Off Cut Thickness [m][w] [A] [m/min] [m] Tin 0.00635 714 54.9 14.8 0.016 Aluminum 0.006352500 75.3 3.8 0.022 Mild Steel 0.003175 1500 63.4 0.2 0.022 Stainless0.003175 2100 86.0 0.25 0.016 Steel

In another aspect, the present invention is directed to a weldingapparatus and a method of welding a workpiece using the apparatus ofFIGS. 1a-1 c. The stream is additionally heated by I²R energydissipation to elevate its temperature to a useful temperature forwelding. Choice of filler material (working material stream) isselected, just as a specific welding rod is chosen in conventionalwelding. The stream velocity (which is governed by the pressure inpressure vessel), the diameter of the nozzle orifice and the orientationof the jetting head to the workpiece and stream temperature (I²R powerdissipation) would be adjusted to set the depth of penetration. Becausethe stream velocity and thus mass flow rate can be varied from very highto very low values, the filler material can be added in much the samemanner as wire in a conventional MIG welding processes, i.e., in azig-zag (weaving) fashion. This allows a wider path of penetration inworkpieces. FIG. 2a shows two pieces of metal (74 a and 74 b) pieceswhich have been prepared for a fillet type weld. Both (74 a) and (74 b)have tapered edges (74 c) which are to be welded together. When thetapered edges are placed in the proper position for welding, the taperededges form a groove (74 d).

FIG. 2b illustrates a welding process using an apparatus of the presentinvention.

Referring to FIG. 2, jetting head (9) and emanating stream (82) aredirected toward the workpieces. The stream (82) makes contact with thetwo workpieces (74 a) and (74 b) somewhere in groove (74 d) along one ofthe tapered edges (74 c). After contact is made, electric current flowsthrough the stream (82), the workpieces (74 a) and (74 b), and back tothe stream heating power supply (54) (not shown in FIG. 2b) throughclamp (55) and lead (53). The stream (82) is heated by I²R powerdissipation, the same as in the case of cutting. As the I²R heatedstream is moved along in relative motion (76) it heats and meltslocalized portions of edges (74 c) as the workpieces (74 a) and (74 b)are being welded together. As the workpieces melt, a molten pool (75 a)is formed by the molten portions of the workpieces and by the metalstream (82). Metal is continuously added to the pool by the stream (82).The amount of material added is controlled by the stream velocity (82 a)and diameter. As weld (75) progresses, some distance behind the weldpool, the welded area begins to cool below the weld area melting pointand solidifies. Although not shown, welding processes will always havesome form of shielding gases flowing around the weld area. Theseshielding gases protect the weld area from oxygen and other undesirableatmospheric contaminants such as nitrogen. Also, the process of thepresent invention allows for the addition of fluxing types of materialsto the working fluid to improve the welding process, either added to theworking fluid while in the heated crucible, or added to the feedstock(87) as an additive compound or laid down as powder as in submerged-arcwelding.

In one embodiment, cutting of non-metallic, non-conductive, andinsulating materials can be accomplished by allowing the molten streamto collect in an electrically conductive pot as shown in FIG. 3. In thisembodiment, it is not necessary for the workpiece to be electricallyconductive. The current path for the stream heating is the same as inFIGS. 1a-1 c except now the current flows through the stream (82), intothe current collection material (83), through current collection vessel(57), through clamp (56) and back through lead (53) to power supply(54). The current collection material (83) can be completely molten oronly partially molten and is made up generally of both the streammaterial and the workpiece material. Additional current collectingmaterial (83) could be added to the current collection vessel (57)separately from the cutting process. An important feature of the currentcollecting material (83) is that it makes good electrical contact withthe stream (82). The I²R heat addition to the stream would still takesplace. The temperature of the stream at the top surface of the workpiececan be controlled, as in the embodiment, by the choice of working fluid,the amount of current passing through the stream, the flow rate of thestream, the diameter of the stream and the length of the stream from theworkpiece to the inlet to the nozzle orifice (5). Workpiece (70) isbeing cut as it passes through the I²R heated stream (82) with relativemotion (72) between the jet head (9) and the workpiece (70). Thisdiffers from the embodiment in that the work piece is not part of theI²R heating circuit.

In another embodiment, an induction heated crucible, as shown in FIG.4a, is used as a possible variation of the implementation of theinvention. In this variation of the jetting head, the crucible heater(30) is replaced with induction heater coils 35 with an incoming coiltube (35 a) and an outgoing coil tube (35 b). The induction heater powersupply and its cooling system (not shown), are used in this embodiment.Also incorporated into the implementation shown in FIG. 4a is the methodof stopping the working fluid flow by use of a levitating force appliedto the working fluid (80) by the induction forces caused by the heatingcoil (35). When a conducting working fluid is placed in an inductionfield, the induced current heats the metal conductor. It also creates anopposing magnetic flux that tends to push the metal working fluid into aregion of lower field strength, i.e., out of the field (or coil). Thispushing force may be computed using the ‘Lorentz’ equation. If theinduced magnetic field is uniform, there is no net force on the workingfluid. A field gradient is needed to provide a lifting force. In oneembodiment, this is accomplished by forming the coil (35) in a conicalshape with the coils near the lower end of the crucible being smaller indiameter then the coils near the upper end of the crucible. In anotherembodiment, this is accomplished by forming the coil (35) with the coilnear the lower end of the crucible in a closer packed relationship thanthe coil near the upper end, as shown in FIG. 4a. This levitating forcecreates a lifting (or levitating) force on the liquid metal fluid whichovercomes the force of gravity acting on the liquid metal, preventing itfrom dripping or leaking. In this design, the stopping of stream (82) iscaused by a combination of changing the pressure in pressure vessel (10)and the applied levitating force of the induction coil; there is no needfor the plug rod (26) arrangement of the embodiment shown in FIG. 1b.The nozzle area is shown in FIG. 4b in the condition of no flow. FIG. 4bshows the liquid to be held in the nozzle orifice without exiting. Thisis due to the levitating forces of the operating induction coil (35).

Also, shown in the embodiment in FIG. 4b is an improvement to theprocess by the addition of gas shielding at the nozzle exit. In thisembodiment, a nozzle disk (12) is held in position by the assemblyconsisting of a shield gas disk (29 a), a down stream portion (29 b),and springs (29 c). Shielding gas flow (27) is applied to the nozzleexit area (29). Shield gas flow (27) flows from the shield gas source(not shown) and flow regulator (not shown) through an on/off valve (28)and connecting lines (28 a) and (28 b) to the nozzle area (29) throughholes (29 d) in the shield gas disk (29 a). The main benefit of gasshielding is to reduce the effects of ambient air on both the workingfluid stream (82) and on the workpiece(s). Although this shielding isnot shown in the embodiment of FIG. 1b it is contemplated that thisfeature would most likely be applied to the embodiment.

In another embodiment, an induction heated crucible and a feedstockheater, as shown in FIGS. 5a and 5 b, are used as a possible variationof the implementation of the invention. In this variation of the jettinghead, the crucible heater (30) is replaced with induction heater coils35, with an incoming coil tube (35 a) and an outgoing coil tube (35 b).The induction heater power supply and its cooling system (not shown),are used in this embodiment. Feedstock wires or rods 87 a and 87 b arefed through electrical contacts 42 a and 43 a and through pressure seals45 a and 45 b. Contacts 43 a and 42 a are electrically connectedelectrical connection wires 43 and 42 respectively. Wires 42 and 43 areconnected to the positive and the negative contacts of power supply 44.The feedstocks 87 a and 87 b are electrically connected together bydriving them down into the conductive fluid 80 contained in crucible 11.The feedstocks 87 a and 87 b are heated resistively by closing contactswitch 44 a of power supply 44. By allowing this initial I²R heating ofthe feedstock 87 a and 87 b, via power supply 44, the overall powerrequirement for the induction heater 35 is reduced. The jet heatingpower supply 54 is connected to the workpiece 70 via clamp 55 and cable53, through switch 54 a, and is connect to the jet 82 via cable 52,which is connected to power supply 44 via cable 43, which is in-turnconnected to the conductive fluid via contact 43 a and feedstock 87 b.It is of course understood that power supply 54 could have beenconnected to the conductive fluid through cable 42 and the otherfeedstock 87 a in the same manner as described.

In one embodiment, a filter 47 is placed in series with the jettingnozzle, the conductive fluid flows first through the filter and thenflows to the nozzle where the jet is formed.

In one embodiment, in place of using a plug rod (26), sealing ball (26a), and actuator (26 c) to prevent fluid flow during the “off”condition, a vacuum source is used to create a “suction” inside thevessel which would overcome the force of gravity acting on the liquid,preventing it from dripping or leaking.

In another embodiment, reversing the polarity of the stream heatingpower supply (54), or using AC power may prove useful in suppressingobserved arcing and sparking on the workpiece surface, and minimizingworkpiece oxidation.

In another embodiment, the present invention features methods ofintroducing the cutting fluid feedstock (87) into the pressure vessel(10) of the jetting head (9) including feeding the feedstock as eitherrod, wire, powder, or liquid metal. In one example, the feedstock isintroduced into the pressure vessel under the full operating pressure.

In one embodiment, the invention features using an electrical currentflow in a stream (jet) of metal to raise the stream temperature. In oneexample, the invention features the use of the liquid metal jet withadded current (I²R heating) for the purposes of cutting and welding.

In one embodiment, the invention features the use of pure metals as thecutting fluids, including iron, aluminum, tin, nickel, titanium, gold,platinum, silver, magnesium, and copper, in combination with the I²Rheat addition process.

In one embodiment, the invention features the use of low meltingtemperature metals having high boiling point temperatures for thecutting fluid, in combination with the I²R energy addition process.Examples of suitable cutting (working) fluid include but are not limitedto: aluminum and aluminum alloys; tin and tin alloys.

In one embodiment, the invention features the use of the beneficialeffects of alloying in the cut, which reduces the melting temperature ofthe workpiece in the vicinity of the metal jet and kerf front, incombination with the I²R heating process.

In one embodiment, the invention features the use of non-meltingadditions to the working fluid, such as, ceramic particles andrefractory metal particles, which would help the cutting process byabrasion and enhancing heat transfer by stirring the interaction zone ofthe jet with the kerf front. The size of particles could range fromabout 0.2 to about 20 microns.

In one embodiment, the invention features the use of the levitatingforce of induction to stop the liquid metal fluid flow from thecrucible.

In one embodiment, the invention features the technique of separatingthe high pressure requirement of a holding vessel from the hightemperature requirement. This is done by placing both the holding vessel(crucible) and its heating source in the pressurizing environment.

In one embodiment, the invention features a technique of cuttingnon-metals or, in general, non-electrically conducting materials usingthe I²R heated liquid stream and by make the electrical connections tothe stream at the up-stream side by contact to the working fluid in thepressure vessel (crucible) and on the down-stream side by contact by thestream to a separate current collection means located beneath theworkpiece.

In one embodiment, the invention features the use of the presentinvention for the purpose of ‘Surface Cladding’ or ‘Surface Welding’,wherein a workpiece is coated (or cladded) with the working fluid. Theworking fluid stream is manipulated so as to coat the workpiece with theworking fluid.

In one embodiment, the invention features the use of the presentinvention for the purpose of ‘3-D Forming’, wherein a three dimensionalstructure is built-up (or formed) from the working fluid. The workingfluid stream is manipulated under computer-code control, so as to builda freestanding, three dimensional structure with the working fluid. Oneprincipal reason why liquid metal jet presents a significant advantageover existing techniques in welding, coating, and forming is that theworking material is liquid. This permits liquid of unique composition tobe formulated in the crucible by supplying several types of feed mixturecan be varied over a much larger range than in the solid state. Whenthis liquid is rapidly cooled to the solid phase at rates of 10³-10⁶K/sec, an alloy with non-equilibrium composition is produced. Thiscomposition can be tailored to create solid materials with uniqueproperties not generally available in conventional materials. As anexample, special magnetic properties can be created in Fe-alloys.High-strength aluminum (and other lightweight metal) alloys can be madethis way due to the refined grain structure that is produced. This isthe technique that gas-assist metal atomization processes use to produceexotic metal powders that are used in the powder metal and thermal sprayindustry. The process of rapid cooling/rapid solidification of liquidmetals is known to those skilled in the art.

The ability to accurately control the location and size of thedeposition spot of the liquid metal jet (apparently, within microns) isan exceptional advantage when compared to existing spray technology thatuses gas jets and powder. Such techniques produce deposition spot sizeson the order of millimeters and suffer from overspray and low depositionefficiency.

Furthermore, the liquid metal jet diameter may be made sufficientlysmall (10′s-100′s of microns) that rapid cooling rates on the order of10³-10⁶ K/sec (often referred to as splat cooling) may be achieved. Theapproximate dimensions of the solidified metal deposit resulting from asingle pass of the liquid metal jet over a surface may be estimated fromdroplet flattening and solidification models. Still another advantage ofthe liquid metal jet is the ability to incorporate particulate, orperhaps even fiber reinforcement into the deposit. The particulate maybe introduced into the molten metal in the crucible, or they may beco-deposited by a second gas jet to the deposition site.

Equivalents

While the invention has been particularly shown and described withreference to specific refered embodiments, it should be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention. For example, other methods of increasing a temperature of ametal jet in addition to those described herein can be used inaccordance with the present invention to modify a workpiece.

What is claimed is:
 1. A method for modifying a workpiece, the methodcomprising the steps of: (a) providing a jet stream comprising anelectrically conductive metallic fluid; (b) coupling an electricalcurrent into the jet stream; (c) providing a shielding gas to the jetstream for reducing the effects of ambient air on the jet stream: and(d) directing the jet stream to the workpiece for modifying theworkpiece.
 2. The method of claim 1 wherein step (b) comprises heatingthe jet stream through ohmic power dissipation.
 3. The method of claim 1wherein step (d) comprises controlling a depth of penetration of the jetstream on the workpiece.
 4. The method of claim 1 wherein step (b)comprises heating the jet stream above a melting temperature of theconductive metallic fluid.
 5. The method of claim 1 wherein step (d)comprises adjusting a velocity of the jet stream.
 6. The method of claim1 wherein step (d) comprises moving the workpiece relative to the jetstream.
 7. The method of claim 1 wherein the step (b) further comprisesheating the jet stream by coupling the electrical current into the jetstream.
 8. The method of claim 1 wherein step (d) comprises one ofcuffing, marking, piercing, or welding the workpiece.
 9. An electricallyconductive metallic fluid jet cutting system for modifying a workpiececomprising: a dispenser comprising a jetting head comprising at leasttwo inlets for receiving multiple feed stocks of an electricallyconductive material, wherein the dispenser is for dispensing a jetstream of an electrically conductive metallic fluid; and a power sourceelectrically coupled to the jet stream for providing electrical currentto the jet stream.
 10. The system of claim 9, wherein a second powersource is connected to at least one feedstock.
 11. The system of claim 9wherein at least one of the feedstocks comprises a wire, bar, or powder.12. The system of claim 9 wherein at least one of the feedstockscomprises iron, aluminum, tin, nickel, titanium, gold, platinum, silver,magnesium, or copper.
 13. The system of claim 9 wherein at least one ofthe feedstocks comprises a plurality of non-melting particles.
 14. Thesystem of claim 13 wherein the non-melting particles are abrasive. 15.The system of claim 9 wherein the jetting head comprises a pressurecontainment vessel.
 16. The system of claim 9 wherein the jetting headcomprises an exit orifice.
 17. The system of claim 9 wherein the jettinghead comprises a nozzle.
 18. The system of claim 17 wherein the nozzlecomprises a disk having a through orifice.
 19. The system of claim 18wherein the disk comprises a material selected from one ofYttria-Stabilized-Zirconia, Magnesia-Stabilized-Zirconia,Calcia-Stabilized-Zirconia, boron nitride-zirconia-silicon carbide,boron nitride, Cubic Zirconia, Alumina, silica, silica composites, andZirconium Diboride.
 20. The system of claim 18 wherein the throughorifice comprises a circular cross section.
 21. An electricallyconductive metallic fluid jet cutting system for modifying a workpiececomprising: a dispenser comprising a jetting head, wherein the jettinghead comprises a crucible, for dispensing a jet stream of anelectrically conductive fluid; a heater coupled to the crucible, whereinthe heater is an induction heater having a characteristic frequency thatcan be calibrated to the level of the conductive fluid; and a powersource electrically coupled to the jet stream, for providing electricalcurrent to the jet stream.